Arc evaporation source

Abstract

The present application provides an arc evaporation source, which includes: a target including a target discharge surface; an arc power supply; an electromagnetic coil configured at a position in front of the target; and a central magnet configured at a position behind the target. The electromagnetic coil forms a first magnetic field including first magnetic force lines intersecting the target discharge surface and extending in a radial inner side of the electromagnetic coil in a front-rear direction. The central magnet forms a second magnetic field including second magnetic force lines extending in the front-rear direction in a region between the central magnet and the target discharge surface. Based on repulsion of the first magnetic field and the second magnetic field, a horizontal magnetic field and a vertical magnetic field are stably formed on the target discharge surface. Accordingly, by promoting movement of arc spots on the target discharge surface, occurrence of macro-particles flying to a workpiece can be suppressed.

Description

Technical Field

[0001] This invention relates to an electric arc evaporation source. Background Technology

[0002] Conventionally, various film-forming methods using arc discharge have been proposed for forming films on the surface of substrates such as tools and machine parts to improve wear resistance. Japanese Patent Publication No. 10-280135 discloses a thin-film evaporation apparatus using such an arc discharge. In this apparatus, arc modulators formed by permanent magnets or electromagnets are respectively arranged in front of or behind the target. A vacuum chamber constitutes the anode of the arc discharge, and a support structure supporting the target constitutes the cathode of the arc discharge. An arc discharge voltage is applied between the two electrodes. Furthermore, magnetic lines of force are formed from the target towards the workpiece (the object to be deposited, the film-forming object) by each arc modulator, causing charged particles of the vapor-deposited material released from the discharge surface of the target by the arc discharge to fly towards the workpiece and accumulate.

[0003] In the technology described in Japanese Patent Publication No. 10-280135, because the arc spot on the target discharge surface is difficult to move, macroparticles (also called droplets) that form the coating material are prone to form. These macroparticles adhere to the workpiece, resulting in a deterioration in the surface roughness of the coating film on the workpiece. Specifically, in the aforementioned technology, permanent magnets or electromagnets disposed around the target material form magnetic field lines with the same orientation passing through the target discharge surface in a direction perpendicular to the target discharge surface. At this time, a strong vertical magnetic field is formed on the target discharge surface, making it difficult to form a horizontal magnetic field. Therefore, the arc spot is difficult to move on the target discharge surface. Consequently, the arc spot tends to remain at the same position on the target discharge surface, and the high-temperature coating material is easily released as macroparticles. Summary of the Invention

[0004] The purpose of this invention is to provide an arc evaporation source that can suppress the generation of macroparticles flying toward the workpiece by promoting the movement of arc spots on the discharge surface of the target material.

[0005] This invention provides an arc evaporation source that utilizes arc discharge to evaporate a coating-forming material and supply the coating-forming material to a workpiece. The arc evaporation source includes a target, an anode, an arc power source, an electromagnetic coil, and a central magnet. The target is positioned behind and facing the workpiece and includes a target discharge surface that releases the coating-forming material forward under arc discharge. The anode is positioned in front of the target to generate the arc discharge. The arc power source applies a discharge voltage between the target and the anode to generate the arc discharge. The electromagnetic coil is positioned in front of the target discharge surface and has a cylindrical shape perpendicular to the centerline of the target discharge surface. This electromagnetic coil forms a first magnetic field. The first magnetic field includes first magnetic lines of force that intersect the target discharge surface and extend in a front-rear direction through the cylindrical space surrounded by the electromagnetic coil. The central magnet is positioned behind the target discharge surface on the centerline to form a second magnetic field. The second magnetic field comprises second magnetic field lines extending in the front-back direction within a region sandwiched between the central magnet and the target discharge surface. The central magnet forms the second magnetic field in such a manner that the orientation of the component of the second magnetic field lines parallel to the center line is opposite to the orientation of the component of the first magnetic field lines parallel to the center line.

[0006] According to the present invention, by promoting the movement of the arc spot on the discharge surface of the target material, the generation of macroparticles flying towards the workpiece can be suppressed. Attached Figure Description

[0007] Figure 1 This is a schematic horizontal cross-sectional view of a film-forming apparatus including an arc evaporation source according to an embodiment of the present invention.

[0008] Figure 2 This is a side sectional view of an arc evaporation source according to an embodiment of the present invention.

[0009] Figure 3 This is an enlarged side sectional view of an arc evaporation source according to an embodiment of the present invention.

[0010] Figure 4 This is a schematic horizontal cross-sectional view of a film-forming apparatus including an arc evaporation source according to a modified embodiment of the present invention.

[0011] Figure 5 This is a diagram showing the magnetic field distribution around the target material in Embodiment 1 of the present invention.

[0012] Figure 6 This is a diagram showing the magnetic field distribution around the target material in Embodiment 2 of the present invention.

[0013] Figure 7This is a diagram showing the magnetic field distribution around the target material in Embodiment 3 of the present invention.

[0014] Figure 8 This is a diagram showing the magnetic field distribution around the target material in Embodiment 4 of the present invention.

[0015] Figure 9 This is a diagram showing the magnetic field distribution around the target material in Embodiment 5 of the present invention.

[0016] Figure 10 This is a diagram showing the magnetic field distribution around the target material of Comparative Example 1 of the present invention.

[0017] Figure 11 This is a diagram showing the magnetic field distribution around the target material in Comparative Example 2 of the present invention.

[0018] Figure 12 This is a diagram showing the magnetic field distribution around the target material of Comparative Example 3 of the present invention. Detailed Implementation

[0019] Hereinafter, a film-forming apparatus 1 comprising an arc evaporation source according to an embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a schematic horizontal cross-sectional view of the film-forming apparatus 1 that includes the arc evaporation source 6 according to this embodiment. Figure 2 This is a side sectional view of the arc evaporation source 6 involved in this embodiment, which is a sectional view including the vertical direction and the front-back direction of the center line CL. Figure 3 This is an enlarged side sectional view of the arc evaporation source 6 according to this embodiment, showing only the portion below the centerline CL. Furthermore, the directions shown in each figure are used to illustrate the structure and function of the arc evaporation source 6 and the film-forming apparatus 1 according to this embodiment, and are not intended to limit the arc evaporation source involved in this invention. That is, the arc evaporation source 6 shown in each figure may also be configured with a different orientation in the horizontal and vertical directions than in each figure. In addition, regarding the front-back direction in each figure, the direction from the target 7 towards the workpiece 4 is defined as the front direction, and the opposite direction is defined as the rear direction. Furthermore, the direction perpendicular to both the front-back and vertical directions is defined as the left-right direction.

[0020] The film-forming apparatus 1 forms a coating (e.g., a nitrided film) on the workpiece 4 (substrate) using a cathode arc discharge. Furthermore, the coating material is not limited to the materials described above. The film-forming apparatus 1 includes a vacuum chamber 2, a rotating stage 3, multiple workpieces 4, a vacuum pump 5, and an arc evaporation source 6.

[0021] The vacuum chamber 2 has walls surrounding an internal space, which is evacuated using a vacuum pump 5. An electric arc discharge is generated inside the vacuum chamber 2. The internal space houses a rotary table 3, multiple workpieces 4, a target material 7, etc. The vacuum chamber 2 is formed of a conductive metallic material; in this embodiment, it is formed of SUS (stainless steel). The vacuum chamber 2 includes: a chamber body 2R that is generally cuboid in shape and has a main space for accommodating the workpieces 4; and a chamber cylindrical portion 2S (chamber cylindrical portion) having a cylindrical space communicating with the main space of the chamber body 2R.

[0022] The chamber cylindrical section 2S contains at least the target material 7, and is centered on the centerline CL ( Figure 2 The target material 7 is connected to the chamber body 2R in a cylindrical shape, with the target material 7 residing in its cylindrical space. Furthermore, the chamber cylinder 2S can be attached to and detached from the chamber body 2R. Additionally, the shape of the chamber cylinder 2S is not limited to the cylindrical shape described above.

[0023] The rotary table 3 is disposed within the chamber body 2R of the vacuum chamber 2. The rotary table 3 has an upper surface capable of holding multiple workpieces 4, such as... Figure 1 As indicated by the arrow, the rotation is achieved using a drive mechanism (not shown) about a rotational central axis extending in the vertical direction. In this embodiment, as... Figure 1 As shown, multiple workpieces 4 are arranged at specified intervals along the rotation direction on the upper surface of the rotary table 3. As an example, each workpiece 4 includes a rotary fixture capable of rotating about a rotation center axis extending in the vertical direction and multiple drill bits mounted on the rotary fixture.

[0024] The arc evaporation source 6 uses an electric arc discharge to evaporate the coating forming material and supplies the coating forming material to the workpiece 4. The arc evaporation source 6 includes a target 7 containing the coating forming material, a back panel 7H, an anode for generating an arc discharge, an electromagnetic coil 8, an arc power supply PS, tubes 9 (main tube 10, distal tube 11, magnetic body 12, inlet tube 13), a yoke plate 14, a central magnet 20, and an outer magnet 30. Furthermore, the target 7, as the coating forming material, can be a material primarily composed of metal or a material primarily composed of carbon; there is no particular limitation.

[0025] The target 7 is positioned behind and facing the workpiece 4, and includes a target discharge surface 7S that releases the coating forming material forward under the influence of the arc discharge. Figure 3 In this embodiment, the target 7 is a flat cylindrical shape, and the target discharge surface 7S corresponds to the front end surface of the target 7. The target discharge surface 7S is a circular shape with a center line CL extending in the front-rear direction. Figure 2 , Figure 3In the diagram, arrow DS indicates the direction in which metal ions, which are the coating material, are supplied toward workpiece 4.

[0026] The back panel 7H is a cylindrical component that supports the target 7 from the rear. The back panel 7H is formed of a conductor and is electrically connected to the target 7.

[0027] The electromagnetic coil 8 is a cylindrical electromagnetic coil positioned in front of the target discharge surface 7S and having a center line CL perpendicular to the target discharge surface 7S. Specifically, the electromagnetic coil 8 is formed by repeatedly winding a coil line (not shown) around the center line CL. The electromagnetic coil 8 receives current from a power source (not shown) and can form a first magnetic field containing first magnetic lines of force that intersect the target discharge surface 7S and extend in a front-back direction through the cylindrical space surrounded by the electromagnetic coil 8. This first magnetic field will be described in detail later.

[0028] The arc power source PS includes a negative electrode connected to the target 7 and a positive electrode connected to the anode, and applies a discharge voltage for generating an arc discharge between the target 7 and the distal tube 11, etc. As a result, the target 7 functions as the cathode of the arc discharge.

[0029] The tube 9 is positioned in front of the target discharge surface 7S and radially inward relative to the electromagnetic coil 8, and has a cylindrical shape centered on the center line CL. The tube 9 includes a main tube 10, a distal tube 11, a magnetic body 12 (magnetic tube), and an inlet tube 13. Furthermore, the tube 9 has a cylindrical internal space that receives the coating material released from the target discharge surface 7S and allows the coating material to pass towards the workpiece 4. Additionally, as... Figure 2 As shown, the tube 9 is arranged in a manner that spans the cylindrical space of the chamber cylindrical portion 2S and the main body space of the chamber body 2R between the target material 7 and the workpiece 4.

[0030] The main tube 10, formed of a conductive non-magnetic material, is positioned in front of the target discharge surface 7S and radially inside the electromagnetic coil 8, and is cylindrical in shape with its center line CL at its center. The main tube 10 has an outer peripheral surface that is radially spaced from the inner peripheral surface of the electromagnetic coil 8. Furthermore, the central portion of the main tube 10 is radially aligned with the electromagnetic coil 8, and the length of the main tube 10 in the longitudinal direction is set to be longer than the length of the electromagnetic coil 8. In other words, the electromagnetic coil 8 is positioned radially outside the main tube 10. Additionally, the inner diameter of the main tube 10 is set to be slightly larger than the outer diameter of the target 7. The main tube 10 is connected to the magnetic body 12 in a conductive manner and forms part of the anode. As an example, the main tube 10 is formed of SUS. The main tube 10 is insulated from the vacuum chamber 2.

[0031] The distal tube 11 is positioned in front of the main tube 10 and is connected to the main tube 10 in a conductive manner. The distal tube 11 has a cylindrical shape centered on the center line CL, and the inner circumferential surface of the distal tube 11 is connected to the inner circumferential surface of the main tube 10. In this embodiment, their inner circumferential surfaces are flush, but this is not a limitation. The inner diameter of the distal tube 11 may also be larger than the inner diameter of the main tube 10. Furthermore, the outer circumferential surface of the distal tube 11 supports a magnetic body 12. As an example, the distal tube 11 is formed of SUS. As described above, the distal tube 11 is connected to the positive terminal of the arc power supply PS ( Figure 1 The distal tube 11 is insulated from the vacuum chamber 2.

[0032] The magnetic body 12 is formed of a conductive magnetic material and is positioned in front of the electromagnetic coil 8, closer to the workpiece 4 than the electromagnetic coil 8. It has a cylindrical shape centered on the center line CL. As described above, the magnetic body 12 is supported (fixed) by the outer peripheral surface of the distal tube 11. In this embodiment, the magnetic body 12 is formed of iron. To be conductive, the magnetic body 12 is preferably a metallic magnetic body other than an insulating magnetic body such as ferrite. The magnetic body 12 is connected to the distal tube 11 in a manner that allows it to conduct electricity and forms part of the anode. Viewed from a direction parallel to the center line CL, the magnetic body 12 has a magnetic inner peripheral surface 12A that is arranged radially inward relative to the electromagnetic coil 8 and surrounds the internal space of the tube. Figure 2 That is, the magnetic body 12 includes a magnetic inner circumferential surface with an inner diameter smaller than that of the electromagnetic coil 8 and surrounding the internal space of the tube. The inner diameter of this magnetic inner circumferential surface 12A is set to be larger than the outer diameter of the target discharge surface 7S. Furthermore, as... Figure 2 As shown, the magnetic body 12 is disposed inside the chamber body 2R. The magnetic body 12 functions to attract the magnetic field (magnetic lines of force) formed by the electromagnetic coil 8 using its magnetic properties. In other words, the magnetic lines of force formed by the electromagnetic coil 8 bend radially outward in front of the electromagnetic coil 8, passing through the magnetic body 12.

[0033] The inlet tube 13 is disposed between the target discharge surface 7S and the main tube 10 in the front-rear direction, and has a cylindrical shape centered on the centerline CL. The inlet tube 13 introduces the coating material released from the target discharge surface 7S into the main tube 10. In this embodiment, as... Figure 2As shown, the inlet tube 13 has a two-stage structure with different outer diameters. The inner and outer diameters of the front portion of the inlet tube 13 are set to be smaller than the inner and outer diameters of the rear portion. Furthermore, the front end of the inlet tube 13 is configured to enter the interior of the main tube 10. Additionally, the inner diameter of the rear end of the inlet tube 13 is set to be larger than the outer diameter of the target discharge surface 7S. Therefore, metal ions released from the target discharge surface 7S can reliably enter the main tube 10. Alternatively, the inlet tube 13 may have the same inner and outer diameters along the longitudinal direction (axial direction). The inlet tube 13 is electrically insulated from the target 7, the main tube 10, and the distal tube 11. As an example, the inlet tube 13 is formed of SUS, but it may also be formed of an insulating material.

[0034] The yoke plate 14 is positioned at a distance from the target material 7 and has a circular plate shape centered on the center line CL. A central magnet 20 and an outer magnet 30 are fixed to the front surface of the yoke plate 14.

[0035] The central magnet 20 is disposed on the center line CL behind the target discharge surface 7S (target 7). The central magnet 20 is a permanent magnet with a cylindrical shape, as in this embodiment, such as Figure 2 , Figure 3 As shown, an S pole is disposed on the front side of the central magnet 20, and an N pole is disposed on the rear side of the central magnet 20. The central magnet 20 is capable of forming a second magnetic field containing second magnetic field lines extending in the front-rear direction within the region sandwiched between the central magnet 20 and the target discharge surface 7S. This second magnetic field will be described in detail later.

[0036] The outer magnets 30 are arranged in a ring around the central magnet 20 radially outward from the central magnet 20, centered on the center line CL, so as to surround the central magnet 20 behind the target discharge surface 7S. In this embodiment, a plurality of permanent magnets are arranged in a ring with spacing between them centered on the center line CL. Each permanent magnet has a cylindrical shape, as in this embodiment, such as Figure 2 , Figure 3 As shown, an N pole is disposed on the front portion of the outer magnet 30, and an S pole is disposed on the rear portion of the outer magnet 30. Furthermore, the outer magnet 30 can be a ring-shaped permanent magnet centered on the center line CL, or it can be a ring-shaped magnetic body magnetized with multiple magnetic poles. However, by arranging multiple permanent magnets in a ring as described above, the cost of the arc evaporation source 6 can be reduced. The outer magnet 30 forms a closed magnetic field between itself and the central magnet 20. In particular, the outer magnet 30 can form a third magnetic field containing third magnetic lines of force extending in the front-rear direction within a region in front of the outer magnet 30 and behind the target discharge surface 7S. This third magnetic field will be described in detail later.

[0037] Furthermore, the yoke plate 14, the central magnet 20, and the outer magnet 30 constitute the magnet unit in the arc evaporation source 6. Additionally, in this embodiment, as... Figure 2 As shown, the central magnet 20 and the outer magnet 30, supported by the yoke 14, are positioned outside the chamber cylinder 2S under atmospheric pressure, but these magnets (magnetic components) can also be positioned inside the chamber cylinder 2S (vacuum chamber 2). Furthermore, in Figure 2 In this diagram, the distance between the central magnet 20 and the outer magnet 30 relative to the target discharge surface 7S is represented by L1, with the rear surface of the yoke plate 14 as a reference. Furthermore, the yoke plate 14 can move a stroke L2 using a drive mechanism (not shown). As a result, due to wear on the surface of the target discharge surface 7S, the central magnet 20 and the outer magnet 30 can move rearward, maintaining a stable magnetic field.

[0038] <Film Formation Process Using Arc Discharge>

[0039] exist Figure 2 In the process, if the internal space of the vacuum chamber 2 is set to a vacuum state by using the vacuum pump 5 and a specified coil current flows through the electromagnetic coil 8, and the arc power supply PS applies a discharge voltage between the main tube 10, the distal tube 11, the magnetic body 12 and the target material 7, then the target material 7 functions as the cathode, and the main tube 10, the distal tube 11 and the magnetic body 12 function as the anode, respectively, and an arc discharge is generated.

[0040] In this embodiment, the magnetic field lines (hereinafter, sometimes referred to as first magnetic field lines) constituting the magnetic field (hereinafter, sometimes referred to as the first magnetic field) formed by the electromagnetic coil 8 in front of the target discharge surface 7S have a forward component. That is, the electromagnetic coil 8 forms a magnetic field (i.e., the first magnetic field) in front of the target discharge surface 7S, and the magnetic field lines (i.e., the first magnetic field) constituting this magnetic field (i.e., the first magnetic field) have a forward component. On the other hand, the magnetic field lines (hereinafter, sometimes referred to as the second magnetic field lines) constituting the magnetic field (hereinafter, sometimes referred to as the second magnetic field) formed by the central magnet 20 disposed behind the target 7 on and around the target discharge surface 7S have a rearward component. That is, the central magnet 20 disposed behind the target 7 forms a magnetic field (i.e., the second magnetic field) on and around the target discharge surface 7S, and the magnetic field lines (i.e., the second magnetic field lines) constituting this magnetic field (i.e., the second magnetic field) have a rearward component. In other words, the magnetic field formed by the electromagnetic coil 8 and the magnetic field formed by the central magnet 20 create a repulsive magnetic field between these two magnetic fields. Therefore, through the magnetic field lines of the target discharge surface 7S, such as Figure 3As shown by arrow D1, when viewed from left to right in the left-right direction, the magnetic field line intersects the target discharge surface 7S at an acute angle. Therefore, a magnetic field component parallel to the target discharge surface 7S (hereinafter sometimes referred to as the horizontal magnetic field) and a magnetic field component perpendicular to the target discharge surface 7S (hereinafter sometimes referred to as the vertical magnetic field) stably coexist on the target discharge surface 7S. Furthermore, at this time, the components of each magnetic field line formed on the target discharge surface 7S that are parallel to the center line CL have the same orientation (in... Figure 2 , Figure 3 (All are facing forward). Furthermore, in reality, Figure 3 The magnetic field lines shown are distributed in a state that is rotated around the center line CL.

[0041] As described above, by stably forming a horizontal magnetic field on the target discharge surface 7S, the moving speed of the arc spot is increased, preventing the arc spot from remaining in the same location. As a result, a portion of the target discharge surface 7S is locally heated, suppressing the generation of droplets and macroparticles, and reducing their size. Consequently, larger or numerous macroparticles are less likely to reach the workpiece 4, improving the surface roughness of the coating film on the workpiece 4.

[0042] On the other hand, electrons released from the target discharge surface 7S of the target 7 by the arc discharge fly from the target discharge surface 7S to the workpiece 4 under the aforementioned vertical magnetic field. Figure 1 Subsequently, most of these electrons, such as Figure 3 Arrow D2 indicates that the direction of the arc discharge is changed to radially outward, thus preferentially reaching the magnetic body 12. As a result, the anode of the arc discharge is stably formed and maintained in the magnetic body 12. Therefore, the position and size of the anode of the arc discharge are difficult to change, and the rise of the discharge voltage of the arc discharge can be suppressed. In addition, as mentioned above, since the main tube 10 and the distal tube 11 also function as anodes of the arc discharge, some electrons also reach these components. However, since the magnetic body 12 attracts the magnetic field formed by the electromagnetic coil 8, the anode can be formed only in the magnetic body 12.

[0043] On the other hand, since the metal ions (cations) released from the target discharge surface 7S have thousands of times the mass of electrons, they cannot follow electrons or move along magnetic field lines. Therefore, as shown by arrow DS, they directly advance towards the workpiece 4 along the radial inner side of the magnetic body 12 and are deposited onto the workpiece 4. Thus, even if the magnetic body 12 is made to attract electrons as described above in order to stabilize the arc discharge, the reduction in the film formation rate of metal ions (cations) on the workpiece 4, i.e., the production efficiency of the film formation process, can be suppressed.

[0044] As described above, in this embodiment, the first magnetic field of the electromagnetic coil 8 and the second magnetic field of the central magnet 20 form a repulsive magnetic field around the target discharge surface 7S. Therefore, this repulsive magnetic field forces the magnetic field lines passing through the target discharge surface 7S to tilt relative to the center line CL, thereby enabling the vertical and horizontal magnetic fields to coexist stably on the target discharge surface 7S. As a result, the horizontal magnetic field allows the arc spot to move actively on the target discharge surface 7S, thereby suppressing the generation of macroparticles and reducing their number and size. On the other hand, the vertical magnetic field allows the metal ions (coating forming material) released from the target discharge surface 7S to stably fly towards the workpiece 4.

[0045] Furthermore, in this embodiment, since outer magnets 30 with opposite polarities are arranged around the central magnet 20 (that is, the outer magnets 30 are arranged around the central magnet 20 with their magnetic poles arranged in the opposite direction to the magnetic poles of the central magnet 20), the magnetic field strength reduction on the target discharge surface 7S can be suppressed by the outer magnets 30 by forming the repulsive magnetic field as described above. In particular, the outer magnets 30 arranged radially outside the central magnet 20 can generate a third magnetic field containing third magnetic field lines with the same orientation as the first magnetic field lines. Therefore, when viewed from the center line CL, a magnetic field connecting the first and third magnetic field lines is formed on the outside of the repulsive magnetic field across the target discharge surface 7S. Therefore, the magnetic field lines that are tilted relative to the center line CL due to the repulsive magnetic field can be attracted to the outer magnets 30, suppressing the instability of the distribution of magnetic field lines (magnetic field) around the target discharge surface 7S, and preventing the magnetic field strength on the target discharge surface 7S from decreasing.

[0046] Furthermore, in this embodiment, since the magnetic body 12 attracts a portion of the first magnetic lines of force radially outward in front of the electromagnetic coil 8, electrons released from the target discharge surface 7S are preferentially guided to the magnetic body 12, thus stably maintaining the anode of the arc discharge on the magnetic body 12. As a result, metal ions can be stably released from the target discharge surface 7S and stably supplied to the workpiece 4.

[0047] In particular, when viewed along the center line CL, the magnetic body 12 has a magnetic inner circumferential surface 12A (inner circumferential surface) that is arranged radially inward relative to the electromagnetic coil 8. Therefore, magnetic lines of force (first magnetic lines of force) passing through the interior of the electromagnetic coil 8 can be more strongly attracted radially outward near the center line CL.

[0048] Furthermore, in this embodiment, the distal tube 11, which is insulated from the vacuum chamber 2, functions as the anode. Therefore, the discharge current does not flow into the vacuum chamber 2, and the arc discharge can be stably maintained. In particular, by making the distal tube 11 the anode, the discharge space can be confined. As a result, the arc discharge is less affected by the state inside the chamber (fouling on the inner wall of the chamber and the arrangement of components), thus enabling stable film formation with high reproducibility.

[0049] Furthermore, in the region between the target 7 and the magnetic body 12, the main tube 10 and the distal tube 11 of the tube 9 are arranged to surround the passage area of ​​metal ions. Therefore, as shown by arrow D3, macroparticles released from the target 7 can be captured, and the macroparticles can be suppressed from reaching the workpiece 4.

[0050] In particular, the cylindrical tube 9 is arranged across the chamber cylinder 2S and the chamber body 2R, so that the metal ions released from the target discharge surface 7S can be stably guided to the workpiece 4 housed in the chamber body 2R, and the generated macroparticles can be more reliably captured by the inner circumferential surface of the tube 9 before reaching the workpiece 4.

[0051] Furthermore, in this embodiment, the main pipe 10 is connected to the magnetic body 12 in a conductive manner and constitutes part of the anode. In this way, by positioning the main pipe 10, which functions as the anode, closer to the target discharge surface 7S relative to the magnetic body 12, an arc discharge can be generated between the main pipe 10 and the target discharge surface 7S when a discharge voltage is first applied, preventing the initial discharge from becoming unstable. Moreover, since the main pipe 10 and the magnetic body 12 are conductive, the anode that discharges the arc after the discharge begins can be controlled within the range from the main pipe 10 to the magnetic body 12. Additionally, the position and range of the anode vary depending on the coil current (magnetic field strength).

[0052] Furthermore, in this embodiment, the inlet tube 13 is disposed between the target 7 and the main tube 10, and the inlet tube 13 is electrically insulated from the target 7 and the main tube 10 (floating, that is, the potential of the inlet tube 13 is independent of the potential of the target 7 and the potential of the main tube 10). As a result, discharge can be performed at a predetermined distance between the cathode and the main tube 10, and the occurrence of abnormal discharge can be suppressed based on this insulation distance.

[0053] Furthermore, in this embodiment, the main tube 10 and the distal tube 11, positioned closer to the target discharge surface 7S than the magnetic body 12, also function as anodes. This promotes discharge between the target discharge surface 7S and the main tube 10 and distal tube 11 when the arc discharge begins. Subsequently, as the discharge stabilizes, the magnetic body 12, located further forward (downstream), preferentially functions as an anode. In this way, by sequentially arranging the main tube 10, distal tube 11, and magnetic body 12 in front of the target discharge surface 7S, separated by an insulated guide tube 13, the arc discharge can be stably maintained, and metal ions can stably reach the workpiece 4. Additionally, as described above, the position and range of the anode also vary depending on the coil current (magnetic field strength).

[0054] The above describes the arc evaporation source 6 and the film-forming apparatus 1 including the arc evaporation source 6 according to various embodiments of the present invention. According to the arc evaporation source 6, by promoting the movement of the arc spot on the target discharge surface 7S, the generation of macroparticles flying towards the workpiece 4 can be suppressed, and their number and size can be reduced. However, the present invention is not limited to these methods. The arc evaporation source 6 according to the present invention can be implemented in the following modified embodiments.

[0055] (1) In the above embodiment, the vacuum chamber 2 is described as having a chamber cylindrical portion 2S, but the present invention is not limited to this embodiment. The vacuum chamber 2 may also be a box-shaped chamber containing the target material 7 to the workpiece 4, and may also contain the central magnet 20 and the outer magnet 30.

[0056] (2) Furthermore, in the above embodiments, it was described that multiple workpieces 4 are arranged on the rotary table 3 and the rotary table 3 rotates. However, the workpieces and their arrangement involved in this invention are not limited to this method, and they can also be arranged in the vacuum chamber 2 in other ways. In addition, the shapes of the workpieces 4, the target material 7, etc., are not limited to the above-described methods. In particular, the target discharge surface 7S of the target material 7 can also be a rectangular, polygonal, or other shape perpendicular to the center line CL.

[0057] (3) Furthermore, the structure and number of tubes 9 are not limited to the above-described manner. In addition, the chamber cylinder 2S of the vacuum chamber 2 can also function as the main pipe 10. In this case, the arc evaporation source 6 may not have tubes 9.

[0058] (4) Furthermore, the construction of the anode of the arc evaporation source involved in this invention is not limited to the above-described manner. Alternatively, other anodes may be provided in front of the target discharge surface 7S instead of the tube 9. Furthermore, the main tube 10 may not function as part of the anode.

[0059] (5) In the above embodiment, it is described that the magnetic field lines (first magnetic field lines) formed around the center line CL of the electromagnetic coil 8 extend forward, while the magnetic field lines (second magnetic field lines) formed around the target discharge surface 7S of the central magnet 20 extend backward. However, their orientations can also be opposite. However, it is preferable to set the direction of each magnetic field line as described in the above embodiment. Furthermore, regarding the relationship between each magnet, the N pole and the S pole can be opposite to each other.

[0060] (6) Furthermore, the arc evaporation source 6 may also lack the outer magnet 30 and only have the central magnet 20. Additionally, the arc evaporation source 6 may also lack the magnetic body 12. In this case, the magnetic fields formed by the electromagnetic coil 8 and the central magnet 20 can be used to promote the movement of the arc spot on the target discharge surface 7S.

[0061] (7) Furthermore, in the above embodiment, it was described that one arc evaporation source 6 is provided in the vacuum chamber 2, but multiple arc evaporation sources 6 can also be arranged in an array. By means of... Figure 2 The chamber cylinder 2S and multiple arc evaporation sources 6 are arranged vertically above and below the chamber body 2R, which facilitates film formation on the workpiece 4. By arranging the magnetic bodies 12 of each arc evaporation source 6 to extend from the chamber cylinder 2S into the chamber body 2R (protruding into the chamber body 2R), mutual interference of magnetic fields between adjacent arc evaporation sources 6 is suppressed. As a result, the orbital disorder of metal ions released from the target material 7 of each arc evaporation source 6 can be prevented.

[0062] (8) Figure 4 This is a schematic horizontal cross-sectional view of a film-forming apparatus 1 including an arc evaporation source 6 according to a modified embodiment of the present invention. In the above embodiments, as... Figure 1 As shown, the positive terminal of the arc power supply PS is connected to the distal tube 11, but the positive terminal of the arc power supply PS can also be connected to the vacuum chamber 2. By connecting the vacuum chamber 2 and the distal tube 11 in a conductive manner, an arc discharge is generated between the target 7 and the main tube 10, the distal tube 11, and the magnetic body 12. Furthermore, in this case, since the vacuum chamber 2 can receive the arc discharge current as part of the anode, it compensates for the functions of the main tube 10, the distal tube 11, and the magnetic body 12 as anodes. In the event that the arc discharge becomes unstable, it prevents excess discharge current from flowing to the main tube 10, the distal tube 11, and the magnetic body 12, thus suppressing their damage.

[0063] Example

[0064] Next, specific embodiments of the present invention will be illustrated. However, the present invention is not limited to the embodiments described below.

[0065] Figure 5 , Figure 6 , Figure 7 , Figure 8 and Figure 9 These are diagrams showing the magnetic field distribution around the targets in Embodiments 1, 2, 3, 4, and 5 of the present invention. Figure 10 , Figure 11 and Figure 12 These are graphs showing the magnetic field distribution around the targets of Comparative Examples 1, 2, and 3 of the present invention. These graphs were obtained by visualizing the magnetic field around the discharge surface 7S of the target material through magnetic field analysis simulation experiments and then simplifying the results.

[0066] <Example 1>

[0067] exist Figure 5 In Embodiment 1 shown, a central magnet 20 and an outer magnet 30 are respectively arranged behind the target material 7. In this case, the front side of the central magnet 20 forms the S pole, and the front side of the outer magnet 30 forms the N pole. As described in the above embodiment, an electromagnetic coil 8 ( Figure 2 A first magnetic field M1 is formed, and a second magnetic field M2 is formed by the central magnet 20 behind the target discharge surface 7S. In addition, a third magnetic field M3 is formed by the outer magnet 30 between the target 7 and the outer magnet 30.

[0068] The first magnetic field M1 contains first magnetic field lines Q1 that intersect with the target discharge surface 7S and pass forward through the interior of tube 9. The component of the first magnetic field line Q1 parallel to the center line CL extends forward. Furthermore, the polarity of the first magnetic field M1 (coil magnetic field) containing the first magnetic field line Q1 in this direction is referred to as the S pole. On the other hand, the second magnetic field M2 formed by the central magnet 20 contains second magnetic field lines Q2 extending rearward in the region between the central magnet 20 and the target 7 (the region surrounded by the projection of the central magnet 20 onto the target 7 along a direction parallel to the center line CL). That is, the component of this second magnetic field line Q2 parallel to the center line CL has the opposite orientation to the component of the first magnetic field line Q1 parallel to the center line CL. Furthermore, the components of the first magnetic field line Q1 and the second magnetic field line Q2 parallel to the center line CL are greater than the components perpendicular to the center line CL. In fact, Figure 5 The situation shown is a state distribution that is rotated around the center line CL. The same applies to the figures described later.

[0069] As a result, a magnetic field M1 and a magnetic field M2 are formed between them, as shown in the figure. Figure 5The repulsive magnetic field is shown. Therefore, the first magnetic field line Q1 near the target discharge surface 7S is inclined in a manner that pushes it outward radially, thereby stably forming the horizontal and vertical magnetic fields as described above on the target discharge surface 7S. In addition, the magnetic field lines through the target discharge surface 7S are directed from the electromagnetic coil 8 ( Figure 2 It tilts toward the central magnet 20 in a radially outward manner.

[0070] Furthermore, in this embodiment 1, the third magnetic field M3 formed by the outer magnet 30 includes a third magnetic field line Q3 extending forward between the target material 7 and the outer magnet 30. That is, the component of the third magnetic field line Q3 parallel to the center line CL has the same orientation as the component of the first magnetic field line Q1 parallel to the center line CL, and the opposite orientation to the component of the second magnetic field line Q2 parallel to the center line CL.

[0071] At this time, as described above, since the magnetic field lines pushed outward in the radial direction around the target discharge surface 7S can be extended in a manner connected to the outer magnet 30, the stability of the magnetic field on the radial outer side of the target discharge surface 7S can be improved.

[0072] Furthermore, in the present invention represented by this embodiment 1, such as Figure 5 As shown, the closed magnetic field extending by connecting the central magnet 20 and the outer magnet 30 remains behind the target discharge surface 7S and does not reach it. In other words, as with known magnetron technology, the orientation of the magnetic field lines formed on the target discharge surface 7S does not reverse in the front-back direction. Therefore, the arc spot on the target discharge surface 7S is significantly constrained without promoting wear on the target discharge surface 7S, enabling stable discharge and release of cations (coating forming material).

[0073] <Example 2>

[0074] exist Figure 6 In Embodiment 2 shown, a central magnet 20 with an N pole is positioned behind the target 7, instead of an outer magnet 30 as in Embodiment 1. In this case, an electromagnetic coil 8 (…) is positioned in front of and around the target discharge surface 7S. Figure 2 The first magnetic field M1 (coil magnetic field) is formed at the S pole, and the second magnetic field M2 is formed by the central magnet 20 behind the target discharge surface 7S.

[0075] Furthermore, similar to Embodiment 1, the component of the second magnetic field line Q2 parallel to the center line CL has the opposite orientation to the component of the first magnetic field line Q1 parallel to the center line CL. As a result, a magnetic field M1 and a second magnetic field M2 are formed as follows: Figure 6The repulsive magnetic field is shown. Therefore, the magnetic field lines near the target discharge surface 7S are tilted in a way that they are pushed outward in a radial direction, thereby stably forming the horizontal and vertical magnetic fields as described above on the target discharge surface 7S.

[0076] <Examples 3 and 4>

[0077] Figure 7 The illustrated embodiment 3, compared to embodiment 1, corresponds to a state where the outer magnet 30 is moved radially inward by 10 mm. Similarly, Figure 8 The illustrated embodiment 4, compared to embodiment 1, corresponds to the outer magnet 30 being moved radially inward by 20 mm. Similarly, the front side of the central magnet 20 forms the S pole, and the front side of the outer magnet 30 forms the N pole. Furthermore, in embodiment 1, the radially outer side surface of the target 7 and the radially inner side surface of the outer magnet 30 are arranged on the same straight line parallel to the center line CL. As shown in embodiments 3 and 4, even when the outer magnet 30 is arranged radially inward relative to the radially outer side surface of the target 7, a repulsive magnetic field can be formed at the center of the target discharge surface 7S, and the magnetic field lines passing through the target discharge surface 7S can be set to intersect the target discharge surface 7S at an acute angle. As a result, the horizontal and vertical magnetic fields described above are stably formed on the target discharge surface 7S.

[0078] <Example 5>

[0079] Figure 9 The illustrated embodiment 5, compared to embodiment 1, corresponds to a state where the outer magnet 30 is moved radially outward by 10 mm. In this way, even when the outer magnet 30 is positioned radially outward relative to the radially outer side surface of the target 7, a repulsive magnetic field can be formed at the center of the target discharge surface 7S, and the magnetic field lines passing through the target discharge surface 7S can be set to intersect the target discharge surface 7S at an acute angle. As a result, the horizontal and vertical magnetic fields described above are stably formed on the target discharge surface 7S.

[0080] Furthermore, in Embodiment 3, Embodiment 4, and Embodiment 5, where the outer magnet 30 was not present, the same horizontal and vertical magnetic fields as described above were also observed to be generated. In this case, to both promote the movement of the arc spot and ensure that the charged particles released from the target discharge surface 7S stably fly towards the workpiece 4, it is preferable to set the radially inner side surface of the outer magnet 30 as follows: a lower limit is a position 20 mm radially inward relative to the radially outer side surface of the target 7, and an upper limit is a position 20 mm radially outward relative to the radially outer side surface of the target 7. More preferably, the radially inner side surface of the outer magnet 30 is set as follows: a lower limit is a position at the same radial direction as the radially outer side surface of the target 7, and an upper limit is a position 20 mm radially outward relative to the radially outer side surface of the target 7. If the above ranges are exceeded, the horizontal magnetic field component on the target discharge surface 7S weakens; therefore, depending on the conditions of the arc discharge, its performance may be relatively weakened.

[0081] <Comparative Example 1>

[0082] Figure 10 Comparative Example 1 shown differs from Embodiment 1 in that it lacks the central magnet 20 and the outer magnet 30. In this case, as... Figure 10 As shown, a first magnetic field line Q1, mainly containing a vertical component, is formed on the discharge surface 7S of the target material. Therefore, it cannot promote the movement of the arc spot, and the generation of macroparticles becomes significant.

[0083] <Comparative Example 2>

[0084] Figure 11 Comparative Example 2, as shown, differs from Embodiment 1 in that it lacks the outer magnet 30, and the first magnetic field line Q1 of the electromagnetic coil 8 and the second magnetic field line Q2 of the central magnet 20 have components with the same orientation (facing forward). In this case, as... Figure 11 As shown, a first magnetic field line Q1, mainly containing a vertical component, is formed on the discharge surface 7S of the target material. Therefore, it cannot promote the movement of the arc spot, and the generation of macroparticles becomes significant.

[0085] <Comparative Example 3>

[0086] Figure 12 The difference between Comparative Example 3 and Embodiment 1 is that although both the central magnet 20 and the outer magnet 30 are present, the first magnetic field line Q1 and the second magnetic field line Q2, like those in Comparative Example 2, have components with the same orientation (facing forward). In this case, as... Figure 12As shown, although a few magnetic field lines intersecting the target discharge surface 7S at acute angles are formed on the target discharge surface 7S, no repulsive magnetic field is formed in the central part of the target discharge surface 7S. Therefore, the movement of the arc spot cannot be promoted. Compared with the embodiments described above, it is difficult to suppress the number and size of macroparticles.

[0087] This invention provides an arc evaporation source that utilizes arc discharge to evaporate a coating-forming material and supply the coating-forming material to a workpiece. The arc evaporation source includes a target, an anode, an arc power source, an electromagnetic coil, and a central magnet. The target is positioned behind and facing the workpiece and includes a target discharge surface that releases the coating-forming material forward under arc discharge. The anode is positioned in front of the target to generate the arc discharge. The arc power source applies a discharge voltage between the target and the anode to generate the arc discharge. The electromagnetic coil is positioned in front of the target discharge surface and has a cylindrical shape perpendicular to the centerline of the target discharge surface. This electromagnetic coil forms a first magnetic field. The first magnetic field includes first magnetic lines of force that intersect the target discharge surface and extend in a front-rear direction through the cylindrical space surrounded by the electromagnetic coil. The central magnet is positioned behind the target discharge surface on the centerline to form a second magnetic field. The second magnetic field comprises second magnetic field lines extending in the front-back direction within a region sandwiched between the central magnet and the target discharge surface. The central magnet forms the second magnetic field in such a manner that the orientation of the component of the second magnetic field lines parallel to the center line is opposite to the orientation of the component of the first magnetic field lines parallel to the center line.

[0088] According to this configuration, the first magnetic field of the electromagnetic coil and the second magnetic field of the central magnet form a repulsive magnetic field around the target discharge surface. Therefore, this repulsive magnetic field forces the magnetic field lines passing through the target discharge surface to tilt relative to the center line, thereby enabling the vertical and horizontal magnetic fields to coexist stably on the target discharge surface. As a result, the horizontal magnetic field allows the arc spot to move actively on the target discharge surface, thus suppressing the generation of macroparticles. On the other hand, the vertical magnetic field allows the coating material released from the target discharge surface to stably fly towards the workpiece.

[0089] In the above configuration, the arc evaporation source preferably further includes an outer magnet, which is disposed behind the target discharge surface and radially outward of the central magnet, and is capable of forming a third magnetic field containing a third magnetic field line. The third magnetic field line is a magnetic field line extending in a front-back direction in a region in front of the outer magnet and behind the target discharge surface. The outer magnet forms the third magnetic field in such a way that the orientation of the component of the third magnetic field line parallel to the center line is the same as the orientation of the component of the first magnetic field line parallel to the center line.

[0090] According to this configuration, the outer magnets arranged radially outside the central magnet can generate a third magnetic field containing third magnetic field lines with the same orientation as the first magnetic field lines. Therefore, by attracting magnetic field lines tilted by the repulsive magnetic field, a magnetic field can be formed around the target discharge surface where the first and third magnetic field lines are connected. Thus, it is possible to suppress the instability of the magnetic field around the target discharge surface due to the occurrence of the repulsive magnetic field, and to prevent a decrease in the magnetic field strength on the target discharge surface.

[0091] In the above configuration, it is preferable to further include: at least one tube disposed in front of the target discharge surface and at a position radially inward relative to the electromagnetic coil, having a cylindrical shape centered on the center line, and surrounding an internal space of the tube for receiving the coating forming material released from the target discharge surface and allowing the coating forming material to pass toward the workpiece, the at least one tube comprising a magnetic tube formed of a conductive magnetic material and disposed in front of the electromagnetic coil in such a way as to attract the first magnetic lines of force radially outward, the magnetic tube constituting at least a portion of the anode.

[0092] According to this configuration, since the magnetic tube can attract the first magnetic lines of force radially outward in front of the electromagnetic coil, the electrons released from the discharge surface of the target material are preferentially guided to the magnetic tube, and the anode of the arc discharge can be stably maintained in the magnetic tube.

[0093] In the above configuration, preferably, the magnetic tube includes a magnetic inner circumferential surface with an inner diameter smaller than that of the electromagnetic coil and surrounding the internal space of the tube.

[0094] According to this configuration, by having a magnetic inner circumferential surface that is positioned closer to the center line relative to the electromagnetic coil, the first magnetic lines of force passing through the interior of the electromagnetic coil can be more strongly attracted radially outward.

[0095] In the above configuration, it is preferable to further include a vacuum chamber for housing the workpiece and the target material, wherein the vacuum chamber is connected to the at least one tube in a manner that is insulated from the at least one tube.

[0096] According to this configuration, since the tube, which is insulated from the vacuum chamber, functions as the anode, the discharge current does not flow through the vacuum chamber, thus maintaining the arc discharge stably.

[0097] In the above configuration, the vacuum chamber preferably has: a chamber body having a main body space for accommodating the workpiece; and a chamber cylindrical portion connected to the chamber body, extending cylindrically about the center line, and having a cylindrical space communicating with the main body space and accommodating the target material, wherein the at least one tube is disposed between the target material and the workpiece in a manner that spans the cylindrical space of the chamber cylindrical portion and the main body space of the chamber body.

[0098] According to this configuration, the cylindrical tube is arranged across the cylindrical portion of the chamber and the main body of the chamber. Therefore, the coating forming material released from the discharge surface of the target material can be stably guided to the workpiece housed in the main body of the chamber, and the generated macroparticles can be more reliably captured on the inner circumferential surface of the tube before reaching the workpiece.

[0099] In the above configuration, preferably, the at least one tube also has a main tube, which is formed of a conductive non-magnetic material and is disposed at a position between the target discharge surface and the magnetic tube in the front-back direction. The main tube is connected to the magnetic tube in a manner that is in communication with the magnetic tube and forms part of the anode.

[0100] According to this configuration, since a main tube, which functions as an anode, is positioned closer to the target discharge surface than the magnetic tube, an arc discharge can be generated between the main tube and the target discharge surface when a discharge voltage is first applied, preventing the initial discharge from becoming unstable. Furthermore, because the main tube and the magnetic tube are connected, the range of anodes in the arc discharge can be controlled according to the coil current after the discharge begins.

[0101] According to the present invention, an arc evaporation source can be provided, which can suppress the generation of macroparticles flying toward the workpiece by promoting the movement of arc spots on the discharge surface of the target material.

Claims

1. An electric arc evaporation source, characterized in that, The coating material is evaporated by an electric arc discharge and supplied to the workpiece. The electric arc evaporation source includes: The target material is disposed behind and facing the workpiece, and includes a target discharge surface that releases the coating forming material forward under the influence of an electric arc discharge. The anode is positioned in front of the target material to generate the arc discharge; An arc power source applies a discharge voltage between the target and the anode to generate the arc discharge; A cylindrical electromagnetic coil, having a centerline perpendicular to the discharge surface of the target material, is positioned in front of the discharge surface of the target material to form a first magnetic field containing first magnetic field lines. The first magnetic field lines are those intersecting the discharge surface of the target material and extending in a front-rear direction through the cylindrical space surrounded by the electromagnetic coil. A central magnet is positioned behind the target discharge surface and on the center line to form a second magnetic field containing second magnetic field lines, wherein the second magnetic field lines are magnetic field lines extending in a front-rear direction within the region sandwiched between the central magnet and the target discharge surface. The central magnet forms the second magnetic field in such a way that the orientation of the component of the second magnetic field lines parallel to the center line is opposite to the orientation of the component of the first magnetic field lines parallel to the center line. At least one tube, positioned in front of the target discharge surface and radially inside the electromagnetic coil, has a cylindrical shape centered on the centerline and encloses an internal space within the tube for receiving the coating-forming material released from the target discharge surface and allowing the coating-forming material to pass toward the workpiece, wherein... The at least one tube includes a magnetic tube formed of a conductive magnetic material and positioned in front of the electromagnetic coil in a manner that attracts the first magnetic lines of force radially outward. The magnetic tube forms at least a portion of the anode.

2. The arc evaporation source according to claim 1, characterized in that... Also includes: An outer magnet is positioned radially outward from the central magnet and behind the target discharge surface to form a third magnetic field containing third magnetic field lines. The third magnetic field lines are magnetic field lines extending in a front-rear direction within a region in front of the outer magnet and behind the target discharge surface. The outer magnet forms the third magnetic field in such a way that the orientation of the component of the third magnetic field line parallel to the center line is the same as the orientation of the component of the first magnetic field line parallel to the center line.

3. The arc evaporation source according to claim 1, characterized in that, The magnetic tube includes a magnetic inner circumferential surface with an inner diameter smaller than that of the electromagnetic coil and surrounding the internal space of the tube.

4. The arc evaporation source according to claim 3, characterized in that... Also includes: A vacuum chamber is provided to house the workpiece and the target material, wherein, The vacuum chamber is connected to the at least one tube in a manner that insulates it from the at least one tube.

5. The arc evaporation source according to claim 4, characterized in that, The vacuum chamber includes: The chamber body has a main space for accommodating the workpiece; and A cylindrical chamber portion, connected to the main body of the chamber, extends cylindrically about the centerline, and has a cylindrical space communicating with the main body space and accommodating the target material, wherein... The at least one tube is positioned between the target and the workpiece in a manner that spans the cylindrical space of the chamber cylindrical portion and the main space of the chamber body.

6. The arc evaporation source according to claim 4 or 5, characterized in that, The at least one tube includes a main tube formed of a conductive, non-magnetic material and is disposed at a position between the target discharge surface and the magnetic tube in the front-to-back direction. The main tube is connected to the magnetic tube in a manner that allows it to conduct electricity with the magnetic tube, and forms part of the anode.

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